1. Field of the Invention
This invention relates to a wire-dot printer, and more particularly, to a printing head of such a printer including actuating devices for driving dot-impact wires or rods comprising, for example, electro-distortion devices. The term "electro-distortion devices" as used herein means a longitudinal-effect electroexpansive transducer in which a strain is reversibly generated by the application of an electrical actuating voltage thereto, causing same to axially, or longitudinally, expand; upon termination of the actual voltage and thus when de-energized, the transducer then compresses, or contracts, in the same, longitudinal or axial direction to its original length. Accordingly, the term "electro-distortion" as employed hereafter in identifying and characterizing the actuating devices in accordance with the present invention will be understood to encompass generically these "electroexpansive" and "electrocompressive" characteristics.
2. Description of the Related Art
Recently, high-speed wire-dot printing heads have become widely used, and accordingly, to drive dot-impact wires of rods of such a high-speed printing head, an actuating means comprising electro- or magnetic-distortion devices has been developed and used instead of the conventional electromagnet type driving elements.
For example, page 92 of "NIKKEI (Japan Economic) MECHANICAL" issued on March 12, 1984, suggests that a printing head including such electro-distortion devices is used. This electro-distortion element is formed by the following steps: preparing a plurality of green sheets made of piezo-electric ceramics, forming a metal paste film on one surface of each of the green sheets to form an inner electrode, and laminating and sintering the plurality of green sheets.
To provide a printing head using such an actuating device, a means for effectively enlarging the very small displacement of such an electro-distortion element is required.